1. Field of the Invention
The present invention is directed to a medical equipment which is in association with off-pump coronary artery bypass and in particular to a perfusion system for off-pump artery coronary bypass which is used for perfusion in relation to a diastolic phase of the cardiac cycle.
2. Description of the Related Art
The coronary artery is an artery which supplies blood to the myocardium and the disease or failure which results from an insufficient supply of the blood to the myocardium is referred to as ischemic heart disease.
The disturbance of blood flow in the coronary artery, one of the causes of the foregoing insufficient supply of blood, is due to formation of stenosis which results from atherosclerosis or deposition of in-blood cholesterol on the inner walls of the artery. Furthermore, such disturbance of blood flow causes a turbulent flow of blood, whereby the artery becomes subject to occlusion. The aggravation of the blood flow disturbance brings an initimal injury, which causes a blood clotting by attracting platelets, resulting in ultimately a full occlusion of the artery.
In addition, though atherosclerosis can be found anywhere in the coronary artery, in general, atherosclerosis is subject to occur at a coronary bifurcation of the artery where the shearing force of the blood flow becomes larger.
Typical examples of coronary artery disease are heart stroke (myocardial infarction) and angina.
The heart stroke occurs due to the necrosis of a portion of the myocardium when the blood to be supplied thereto is decreased or completely stopped as a result of the artery occlusion. This phenomena is medically called myocardial infarction. This is a serious symptom which occurs suddenly. This symptom is accompanied by perspiration and/or shock, and results in unconsciousness sometimes. When the heart stops completely due to heart stroke, such a phenomena is said to be cardiac arrest which leads to death.
The degree of necrosis varies depending on the amount of the affected myocardium. Due to the fact that the damaged myocardium releases a kind of enzyme into the blood, measuring the activity of such enzyme makes it possible to provide an index which indicates what degree the myocardium is damaged.
The heart stroke does not occur always due to a physical fatigue or mental fatigue or both. Unlike the case of an angina, the condition of heart stroke is not always reduced even though the patient relaxes or rests.
On the other hand, the onset of angina is due to insufficient or decreased supplies of oxygen and glucose resulting from insufficient blood supply to the myocardium as a result of the coronary artery occlusion. In such a case, the heart begins to try to generate energy through a chemical process which differs from that when sufficient blood supply is made. However, such a chemical process produces waste products which can not be excluded by a smaller amount of blood and such waste products become a cause of pain. Typically, the condition of angina appears as a tense, constricting pain at a lower portion of the breastbone or sternum. Due to the fact that such the condition is related to physical activity of the patient, taking a rest eases the pain.
Where the condition of either myocardial infarction or angina becomes worse, a coronary revascularization has to be made on the occluded or stenosed coronary artery. The coronary revascularization is divided into two types or categories: (a) intervention treatment through percutaneous transluminal coronary angioplasty (PTCA) and (b) surgical treatment through coronary artery bypass graft (CABG).
(a) Intervention treatment through percutaneous transluminal coronary angioplasty (PTCA) is a method of expanding the cross-section of the stenosed portion of the coronary artery with the usage of a balloon catheter. This method is suitable for the patient who has only one stenosed portion of the coronary artery and who can not bear a surgical operation due to a disease such as pulmonary disease in its worst condition.
(b) Surgical treatment through coronary artery bypass graft (CABG) is a surgical technique to bypass the occluded or stenosed vessel. This treatment is suitable for application on a highly stenosed or occluded coronary artery of a patient where it is impossible to perform percutaneous transluminal coronary angioplasty (PTCA) or where there are a plurality of occluded portions in the coronary artery. The details of this technique will be described hereinafter with reference to FIGS. 11(a) and 11(b).
Surgical treatment through coronary artery bypass graft (CABG) is classified into two methods: so-called ‘in situ arterial grafting’ and so-called ‘bypass grafting’. As shown in FIG. 11(b), in general, ‘bypass grafting, a bypass tube 25a using a lower extremity separated saphhenous vein graft (SVG) is anastomosed to a proximal side (aorta side) and an anastomosis 27 at a downstream side of a stenosed or occluded portion 26 of a target coronary artery 27, thereby bypassing the blood to the distal side of the coronary artery. As shown in FIG. 11(a), in ‘in situ arterial grafting’ which is a blood supply method by way of different passage, an appropriate arterial blood vessel such as a bypass tube 25 using an internal mammary artery (ITA) is led for anastomosis to a distal side of a coronary artery.
Because the saphenous vein graft (SVG) used in ‘vein grafting’ has to accommodate a venous valve, the long range graft patency is not very good, and therefore recently, employing ‘in situ arterial grafting’ has become the mainstream operation. In addition, some doctors employ so-called ‘free arterial grafting’ which is established, like so-called ‘saphenous vein graft,’ in such a manner that proximal and distal sides of a separated arterial vessel is anastomosed to the aorta side and the coronary artery side, respectively. In this method, though the arterial vessel is used as grafting material, due to the fact that the intimal cells of the arterial vessel after separation thereof die, the merit of this method is better than ‘vein grafting’ but falls far behind ‘in situ arterial grafting’.
Even when such ‘in situ arterial granting’ is employed which is an outcome of the latest medical technology, the suture of the coronary artery having a small diameter which ranges from 1 mm to 2.5 mm inclusive has to be done in very precise fashion and the blood flow to the anastomosed portion has to be stopped. Thus, so-called ‘in situ arterial grafting’ is compelled to be practiced under the condition of cardiac arrest with the usage of extracorporeal circulation. The steps of such an under cardioplegic arrest bypass operation using the extracorporeal circulation are as follows:
First of all, a pre-treatment is made on the patient. While the patient is being anesthetized, the breast is opened by incising the breast along the breast bone or sternum and subsequent the same is cut. Thereafter, the pericardium which surrounds the heart is exposed. Simultaneously, an internal mammary artery is separated or a portion of a vein is extracted from the lower extremity. The patient is given heparin. Cannulas are fitted into the ascending aorta and the right atrium, respectively, and the patient is secured with a pump-oxegnator system. The blood of the patient is fed to the pump-oxegnator system for filtering. An oxygen supply device and the extracorporeal circulation provide oxygen to the patient. The aorta is clamped in order that the blood can not reach the heart. A cardioplegia solution is injected into the patient for arresting the heart. While the heart is being arrested, the blood circulation is maintained by the extracorporeal circulation. The surgeon anastomoses a vein or artery between the aorta and a distal side of the occluded or stenosed portion of the coronary artery for bypassing the occluded or stenosed portion. One or more similar bypass operations are made when there are one or more other occluded or stenosed portions of the coronary artery. Immediately upon completion of the operation and anastomosis, the breast is closed after separation of the extracorporeal circulation from the patient. The patient is transferred to a recovery room and several days are required for beginning the extubation of a tube in the trachea.
Though the foregoing under-cardioplegic arrest coronary artery bypass operation can be made without limitation of time and makes it possible to anastomose in stable fashion on the outer surface of the heart which is being made to be stationary, serious risks and problems have been pointed out. In detail, due to the fact that the coronary artery bypass operation is made under cardioplegic arrest, the aorta clamping and the extracorporeal circulation which are essential factors for the under cardioplegic arrest coronary artery bypass operation sometimes may exert a bad influence on the patient such as physical injury of the vessel, hemorrhage tendency, or insufficient supply of oxygen. For example, patheopoiesis risks of cerebral infarction, hemorrhage compliance, infection of the incision of the sternum, pneumonia, renal failure and so on can occur. Inflammatory response of the whole body of the patient raises a problem which results from the destruction of immunity and complement system of the human body when using the extracorporeal circulation. In addition, the required blood transfusion for the supplementation of the blood and blood component lost in the extracorporeal circulation sometimes becomes causes of increasing risks of AIDS and other infections.
Moreover, the extracorporeal circulation per se is very expensive to purchase and cumbersome to operate, which results in that only large scale medical institutions can use the extracorporeal circulation. In addition to this, the national interest on increasing medical care expense is being raised. Thus, developing a new technology is demanded which is capable of eliminating iatrogenic complication.
In view of such circumstances, in about 1994 in Western countries, off-pump coronary artery bypass which is made while the heart is beating was proposed and recently in Japan, off-pump coronary artery bypass has been attempted. In this off-pump coronary artery bypass, no operative wound for connecting the extracorporeal circulation is required, the patient is invaded with little medicine such as heparin when using the extracorporeal circulation, which prompts the patient's postoperative recovery. For example, conventionally, the postoperative patient is required to be kept under a strict watch for a duration of 3–7 days in the intensive care unit (ICU) and subsequently about a 1 month medical treatment in the general ward. Moreover, about 2-months of care is required before his/her rehabilitation. On the contrary, according to the newly proposed method, a medical report says that only a few days are required before leaving the hospital after the operation and one week after the operation the patient can attain his/her rehabilitation. In addition, it becomes possible to reduce the risks of blood dilution and air embolism which are inevitable when using the extracorporeal circulation. Moreover, the bleeding amount during operation can be decreased, thereby enabling the amount of blood transfusion to be reduced. Of course, the patient becomes free from pains and suffering during the training for the rehabilitation. No very expensive materials for artificial heart are required.
An example of the procedure of the foregoing off pump coronary artery bypass is as follows: While the patient is in the anesthetized condition, a target coronary artery is exposed by a median sternotomy or a 10 cm incision of the 4th intercostal space. Thereafter, a bypass tube is prepared and at an upstream side of a portion to be anastomosed of the target coronary artery is tied or fastened with a thread. With a fixing device, only the operation field on the beating heart is fixed. Thereafter, the portion to be anastomosed of the target coronary artery is incised for the anastomosis with an internal mammary artery or a saphenous vein with the usage of a very, very thin nylon thread. When the operation and the anastomosis are completed, the tied portion is released by removing the thread therefrom and the incised portion is closed after applying a protamine to the patient. The in-trachea tube is extracted from the patient such that the patient can be removed from the operation table, the patient is transferred to a recovery room, and some days later the patient is able to leave the hospital.
As described above, the foregoing off pump coronary artery bypass has become notable as an innovative approach. However, some risks and problems have been pointed out.
In the operation which is made while the heart is beating, due to the fact that the vessel of small diameter is incised on the outer surface of the heart which is being vibrated continually by the heart beating, the incision is not easy to practice. In addition, due to heavy bleeding as a result of such an incision, it becomes difficult to watch the portion to be anastomosed, which makes the anastomosis difficult to do. Moreover, tying the upstream side of the portion of the vessel to be anastomosed for the bleeding arrest causes, due to the resulting insufficient blood flow, a myocardial ischemia, which may result in a cardiac arrest. Thus, the anastomosis has to be done very quickly and very surely or precisely, which limits the use of this method. Also, this method requires an additional pre-treatment for about several minutes such as a pre-conditioning (a condition check by temporal arrest of the vessel) before the operation is initiated.
Such risks and problems can be removed by placing, like the conventional operation, experts of extracorporeal circulation and blood transfusion, thereby becoming costly.
Thus, to improve the foregoing unsatisfactory facts resulting from the myocardial ischemia, it is believed that perfusing the arterial blood to a downstream side near the portion of the coronary artery to be anastomosed is preferable. In order to realize such a perfusion, an idea has been proposed wherein one end of a tube is inserted into the femoral artery and the other end is inserted into a specific portion of the coronary artery for the purpose of perfusion using the patient's own blood flow. However, in this idea, the tube which has to be inserted into the coronary artery is required to be thin in diameter, which makes the flow restriction of the pipe higher, resulting in that the amount of blood flow becomes insufficient. U.S. Pat. No. 5,066,282 proposes a perfusion device having a blood injection pump which is out of synchronization with the heart beat. However, in the continual perfusion method which is made out of synchronization with the heart beat, the perfusion is made under compulsion and under high pressure within the closed coronary artery whose upper end is isolated. Thus, such method is non-physiologlcal and may, contrary to the purpose, cause a risky condition.